AWS CloudWatch GetMetricsData: "Sum" misses points on periods without values

Question

I am querying GetMetricsData from AWS CloudWatch:

                 {
                    StartTime: lastWeek ,
                    EndTime: today,
                    MetricDataQueries: [
                        {
                            Id: 'invocations',
                            Label: 'Invocations',
                            MetricStat: {
                                Metric: {
                                    Dimensions: [
                                        {
                                            Name: 'FunctionName',
                                            Value: /* FunctionName */,
                                        },
                                    ],
                                    MetricName: 'Invocations',
                                    Namespace: 'AWS/Lambda'
                                },
                                Period: 60*60*24, // day
                                Stat: 'Sum',
                                Unit: 'Count',
                            },
                        },
                    ],
                }

This is what I get:

Instead of getting data for 7 days (i.e. a week) I get 5 days. I have 2 missing days (as you can see in the graph).

Those missing days did not have any data.

CloudWatch is not returning points which have no data. How can I make the Sum operation return the actual count (0) instead?

Answer 1

You can use metric math and FILL function to default missing values to 0.

Id of your metric is invocations so the expression would be:

FILL(invocations, 0) 

Full query would be something like:

             {
                StartTime: lastWeek ,
                EndTime: today,
                MetricDataQueries: [
                    {
                        Id: 'result',
                        Label: 'Sums with zeros',
                        Expression: 'FILL(invocations, 0)'
                    },
                    {
                        Id: 'invocations',
                        Label: 'Invocations',
                        MetricStat: {
                            Metric: {
                                Dimensions: [
                                    {
                                        Name: 'FunctionName',
                                        Value: /* FunctionName */,
                                    },
                                ],
                                MetricName: 'Invocations',
                                Namespace: 'AWS/Lambda'
                            },
                            Period: 60*60*24, // day
                            Stat: 'Sum',
                            Unit: 'Count',
                        },
                    },
                ],
            }

This will return 2 metrics, with zeros and without. You can then hide the original metric by setting ReturnData: false in that MetricDataQuery.

See here for more details:

• https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/API_GetMetricData.html

• https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/using-metric-math.html